In recent years, the need for network solutions providing quality of service in high bandwidth applications has evolved as a result of the increasing demand for transfer of, e.g., real-time speech, video and multimedia over networks such as the Internet.
The use of circuit switched networks, which have the inherent property of providing each host with a guaranteed bandwidth, has been found to provide many advantageous features in this context.
A new circuit switched network solution, which has received much interest over the last few years, is known as DTM (Dynamic synchronous Transfer Mode). In a DTM network, circuit switched isochronous channels may be dynamically established, modified, and terminated based upon changes in user capacity requirements.
An advantage with DTM is that the bandwidth of an established isochronous channel may be dynamically changed by the allocation or deallocation of time slots to said channel. However, changing the bandwidth of an existing channel requires synchronization between sender and receiver(s), as well as intermediate nodes, to avoid losing data (in case the sender increases the number of slots allocated to a channel before the receiver does), or to avoid receiving garbage data (if the receiver increases the number of slots allocated to said channel before the sender does).
Different suggestions have been made of how to arrange the necessary bandwidth change synchronization to avoid these problems. One suggested solution has been to simply stop sending data while the bandwidth change is being performed. However, this means that the channel is unused during a period of time, thus inevitably leading to a waste of bandwidth resources. Another suggested solution has been to ensure that the bandwidth change is being made simultaneously at sender, receiver, and any intermediate nodes, by numbering the network frames and, using control signaling for agreeing on which specific frame to effectuate the change. This of course has the drawback of requiring extra signaling and the provision of an often complicated frame counting mechanism.
In view of the above, an object of the invention is to provide a simple, reliable, safe and effective mechanism for synchronizing bandwidth changes in a circuit switched networks of the kind mentioned in the introduction, especially in a DTM network.